The present invention relates to apparatus for manipulating sheet-like blanks, particularly for making and transporting blanks in packing machines for cigarettes or the like. Still more particularly, the invention relates to improvements in apparatus for supplying a continuous succession of paper, plastic or metallic blanks to a conveyor, especially to a turret-like, chain-like or belt-like mobile carrier of entraining elements for discrete blanks.
It is known to produce a succession of blanks for conversion into components of cigarette packs or the like by drawing a web of metallic foil, paper, lightweight cardboard or synthetic plastic material from a bobbin or reel and by severing the web at regular intervals so that the web yields a succession of blanks which are thereupon converted into components of packs, either by draping the blanks directly around arrays of smokers' products or by draping the blanks around suitable mandrels. As a rule, the web is drawn from the bobbin or reel at a constant speed and without interruptions, but the conversion of its foremost portion into a succession of blanks takes place at regular or irregular intervals in synchronism with normally intermittent movements of entraining elements (packs or mandrels) on the mobile carrier. Therefore, a portion of the uncoiled web is normally caused to form an intermediate supply from which the material is being drawn prior to the making of a blank.
In order to avoid an interruption in the feed of blanks to the carrier when the supply of running web is exhausted, the just described apparatus normally comprises a splicer which attaches the leader of a fresh web to the trailing portion of the running web before the supply of running web is exhausted. This insures that the packing machine need not be arrested whenever the supply of running web is exhausted. The means for splicing may comprise a device which attaches adhesive-coated uniting bands to the trailing portions of running webs and to the leaders of fresh webs. That pack which includes a component or layer made of a blank which contains a splice (i.e., a uniting band) s segregated from the other packs before the packs are introduced into storage, into cartons or into other types of receptacles. A drawback of the just described apparatus is that the packing machine must be provided with a detector for packs which contain uniting bands and that the number of such defective packs is quite substantial, especially in a modern high-speed packing machine which can process the output of several cigarette markers each of which can turn out up to and in excess of 70 cigarettes per second.
German Offenlegungsschrift No. 2,205,366 discloses a modified apparatus wherein the fresh web is held in a position of readiness and begins to advance into the range of a severing device as soon as the supply of running web is exhausted to a predetermined extent. Each web is advanced stepwise by a separate drive, such as by discrete pairs of rollers or wheels, and the changeover from advancement of the running web to advancement of the fresh web takes place during an interval which is shorter than the interval between two successive advances of the running web. The just described apparatus need not resort to a splicer, and the entraining elements of the mobile carrier invariably receive satisfactory blanks. However, this apparatus also exhibits a number of drawbacks, particularly because the leader of the running web is pushed through the device which is actuatable to sever the running web at predetermined intervals in order to convert the front portion of the running web into a succession of discrete blanks. In other words, that portion of the running web which extends beyond the severing device is not guided and is therefore likely to curl, fold or to be otherwise deformed, especially if the web consists of extremely thin synthetic plastic material which is used for the making of transparent outer envelopes having customary tear strips. In fact, even the provision of channels, rails or analogous guide means cannot insure undue and unpredictable deformation of the foremost portion of a web which consists of cellophane or a lightweight metallic or paper sheet stock.
German Offenlegungsschrift No. 1,932,360 discloses a further apparatus wherein the two webs are attracted by two discrete suction drums and are severed while adhering to the respective drums. The thus obtained blanks are thereupon transferred onto a further conveyor which delivers them into the path of entraining elements on the aforementioned mobile carrier. One of the webs is continuously fed to the respective suction drum by a pair of driven rollers while the rollers for the other (fresh) web remain idle. The just described apparatus operates satisfactorily; however, its initial and maintenance costs are extremely high, not only because the apparatus employs two discrete suction drums but also because the apparatus must be provided with two discrete severing devices, one for the web which adheres to the other drum. Still further, the transfer of blanks from the suction drums onto the further conveyor must be effected by a complex mechanism which is prone to malfunction. Moreover, the controls of the apparatus are quite complicated, especially if the apparatus is to insure that the last blank made from an expiring web is followed, without delay, by the first blank which is obtained in response to severing of the fresh web.